But the authority yesterday cautioned those who had been given blood not to worry, saying that the chance of virus carriers developing cancer was 'very low'.

The five patients had been counselled on their condition and monitoring would continue. None of them showed signs of disease, a spokesman said.

A Hong Kong woman who tested positive for the rare virus, HTLV-1, died of an unusual cancer at the end of last year.

HTLV-1, or human T-cell leukaemia lymphoma virus-1, is endemic in southwestern Japan. It can cause the deadly blood cancer adult T-cell leukaemia or debilitating neurological illnesses as much as 30 years after infection.

Although it is a member of the same family as HIV, it does not cause AIDS, according to the authority. It is transmitted in the same way as HIV - through blood transfusion, sexual intercourse, breast milk or intravenous drug use.

It is not known how the woman who died contracted the virus.

The Red Cross Blood Transfusion Service began screening donated blood for the virus last December. After it found three of more than 100,000 donors since 1986 were carriers, it began a search in July for patients who had received the infected blood.

The blood from the donor carriers has been thrown away, but the Red Cross admits that more may be found as it continues tests.

But the Hospital Authority spokesman said: 'The life-time risk of [those carrying the virus] developing the disease is very low.'